I am trying to get an understanding of exactly what I need to do to get both phones working. I have a 4S on the way and am currently using the 4. We used my fiancée's upgrade so as I understand it, the Sim card is programmed for her phone. If we activate it, it will make her current dumb phone sim card useless. If I swap my iPhone 4 sim into the new 4S before activating and put the new sim into my old (but returned to default) 4, will everything work properly? We both have the same exact plan, but will it cause issues that they show she has a 4S but in reality she is using the 4? Thanks in advance!